The scaling resistance of slag-blended cements can be critical when tested according to the procedure described in the present ASTM C 672 standard. As soon as slag replacement is greater than 20 percent, the scaling resistance of concretes made with a slag-blended cement deteriorates rapidly. But when the initial water curing procedure is lengthened from 13 to 27 days, the slag-blended samples have enough time to become more fully mature and they easily pass the scaling test, even when the substitution rate is as high as 80 percent. Lengthening of the present initial water-curing period from 13–27 days should be considered in the case of slag-blended cements, and most probably for other blended cements as well. This would allow for concretes made with a blended cement to reach the same degree of maturity as concretes made with pure Portland cement when they are submitted for the first time to freezing and thawing cycles in the presence of deicing salts.